This invention relates to a television receiver incorporating a horizontal output deflection circuit which implements the proper drive control for the output transistor automatically depending on the high-voltage output capacity.
The horizontal deflection circuit in a television receiver operates to swing the electron beam and left in the cathode ray tube in response to a sawtooth wave current of about 15,750 Hz supplied to the horizontal deflection coil. The horizontal deflection circuit basically comprises a horizontal oscillation circuit, a horizontal drive circuit and a horizontal output circuit, as shown in FIG. 1. In addition, the horizontal deflection circuit includes a synchronous AFC circuit, high-voltage generation circuit, power supply circuit, etc.
Generally, in order to operate stably the output transistor which forms the horizontal output circuit, a base current greater in value than the collector current, which fits the high-voltage capacity, divided by the d.c. current gain of the transistor is fed to the base. Namely, the output transistor is operated in over-drive mode. On this account, conventional television receivers are provided with a heat sink having a cooling ability to meet the high-voltage capacity and characteristics of the transistor.
The above-mentioned horizontal drive and horizontal output circuits are arranged as shown in FIG. 2. In the figure, indicated by Tr.sub.1 is a transistor which forms the horizontal oscillating circuit, Tr.sub.2 is a transistor which forms the horizontal drive circuit, and Tr.sub.3 is a transistor which forms the horizontal output circuit.
In order to bring the output transistor Tr.sub.3 quickly into a state of saturation (ON) or a state of cutoff (OFF), a sufficient base current must be fed. Therefore, an amplifying circuit is configured between the oscillation circuit and output circuit so that the pulse voltage is rendered the amplification and waveform shaping before it is delivered to the output circuit. This amplifying circuit is called "drive circuit", and it is generally an emitter-grounded transformer-coupled amplifying circuit as shown in FIG. 2. The driving transistor Tr.sub.2 operates as a switching element as in the output circuit, and it is OFF when the output circuit is ON, or it is ON when the output circuit is OFF, so that the driving transformer is always loaded by one of the transistors Tr.sub.2, Tr.sub.3.
However, the conventional arrangement is designed to operate the output transistor stably by feeding a base current greater in value than the collector current, which fits the maximum high-voltage output capacity, divided by the minimum d.c. current gain of the transistor Tr.sub.3 by means of the driving transistor Tr.sub.2, and therefore in an operating condition of a minimal high-voltage output capacity and a maximal transistor d.c. current gain in combination, an excessive base current creates an increased collector loss and a temperature rise at the semiconductor junction section, which necessitates a large heat sink having a small thermal resistance in order to operate the transistor stably and safely, resulting in an increased cost and awkward packaging.